1. Field of the Invention
This invention relates to fuel injection systems for spark ignited, internal combustion engines of the type which monitor engine operating parameters and control a fuel charge to the engine as a function of those parameters and, more particularly, to such a system which provides an enrichment of the fuel charge during engine warm-up and increases that temperature sensitive enrichment during transient increases in engine load during warm-up.
2. Prior Art
Fuel injection systems which measure the operating parameters of a spark ignited, internal combustion engine and meter quantities of fuel controlled by the measurements to the engine cylinders have been in limited use for a number of years. Recent government regulations limiting the permissible quantities of atmospheric pollutants which may be present in vehicle engine exhausts and recent increases in petroleum costs have increased interest in these fuel injection systems as alternatives to conventional carburetors because of their superior ability to control the fuel flow to the engine. A fuel injection system in which the present inventor may be used and which has the ability to control the engine fuel flow to maintain the engine air to fuel ratio at a desirable value to minimize exhaust pollutants with acceptable fuel economy is disclosed in my United States patent application Ser. No. 629,421 entitled "Fuel Injection System" and filed on Nov. 6, 1975 now abandoned.
Injection systems typically control the quantity of liquid fuel that is provided to the engine but this fuel must be vaporized before the combustion reaction can take place. The vapor air to fuel ratio rather than the liquid air to fuel ratio provided by the fuel system determines the combustion process. The relationship of the liquid versus vapor air to fuel ratio depends on the volatility of the fuel, as well as fuel temperature and pressure. Volatility refers to the ease with which the fuel passes from the liquid into the vapor phase. If the injector system is well designed under certain operating conditions, such as cruising speed with a fully warmed-up engine, the entire injected fuel charge may be fully vaporized but, under other conditions, such as during acceleration of a relatively cold engine, an appreciable portion of the liquid fuel charge may not become vaporized and the injected quantity of fuel therefore must be augmented, that is enriched, to insure sufficient vaporized fuel to prevent the engine from stalling.
Fuel enrichment during engine warm-up is normally provided in many fuel injection systems. For example, my copending U.S. patent applications, Ser. No. 629,348 entitled "Fuel Injection System With Warm-Up Circuit," now abandoned, and Ser. No. 629,443 entitled "Control Computer for a Fuel Injection System," now U.S. Pat. No. 4,058,709, both filed on Nov. 6, 1975, disclose a fuel injection system employing a thermistor to monitor engine temperature and provide fuel enrichment to the engine during warm-up for engine temperature below normal operating conditions.
The fuel injection system disclosed in U.S. Pat. application Ser. Nos. 629,348 and 629,443 also employs a sensor which measures manifold pressure, which may be manifold vacuum, and modifies the fuel charge provided to the engine as a function of the manifold pressure to maintain the proper air to fuel ratio. In air throttled engines, an increased power demand by the engine occurs when a sudden decrease in manifold vacuum results from a sharp depression of the accelerator or a sudden increase in engine load, such as may be caused by shifting the engine from neutral into gear. The fuel injection system responds to such decrease in manifold vacuum by increasing the fuel charge provided to the engine. At normal engine operating temperatures, this increased fuel charge may be fully vaporized to provide the engine with the full fuel charge necessary to respond to the increased power demand. But, at lower engine operating temperatures, the fuel charge provided in response to a sudden decrease in manifold vacuum may not be fully vaporized and the resulting vaporized portion of the fuel charge may not be sufficient to allow the engine to meet the increased power demand without excessive exhaust emissions.
To avoid this situation, previous fuel systems have been designed to provide an adequate air to fuel mixture during cold engine conditions so that sufficient vaporized fuel will be present to allow the engine to respond to transient load increases during warm-up. However, such air to fuel mixture provided during warm-up transient load increases may be overly rich for the more or less steady state lighter engine load conditions. Such overly rich mixture under more or less steady state lighter engine load conditions will sharply increase emission of hydrocarbons and carbon monoxide from the engine. Catalytic convertors do not adequately solve this problem because they are not in full operation during warm-up.